Yes, go to Ivris and take a look at her Reagents, you'll see that each one lets you target a particular body part. Combine that with whatever item corresponds to the transformation you want and refine the two together. Now you have a much more targeted transformation. For example, a Blue Egg plus a Turgid Mushroom will cause you to grow a penis if you don't already have one, or lengthen one if you do.
A basic element of the system is that the Blue and Pink Eggs have opposite effects due to being the general 'masculine' and 'feminine' items, so if you want to increase some trait associated with the former (ie penis size) or decrease a trait associated with the latter (breast size) you'd use a Blue Egg with the appropriate reagent and vice versa. Pink Egg+Turgid Mushroom reduces penis size (and can remove it completely so long as doing so wouldn't leave you with no genitals) while Pink Egg+Wild Melon increases breast size.
